The invention relates to granular materials used as carriers for pesticides, soil amendments, and as animal bedding (e.g. cat litter). Such granular materials are typically 1 to 1.5 millimeters in average particle size (approx. US mesh 8×16), with a bulk density less than 65 pounds per cubic foot (pcf) and with an RTA (weight % resistance to attrition) of at least 85%.
Granular materials formed by agglomeration of powdered ingredients often use organic polymers to bind the fine ingredient particles into granules. The resulting granules or pellets may be dispersible or non-dispersible depending on the properties of the organic polymer binder agent.
There can be adverse reactions between the organic polymer binders and “active agents.” Water borne active agents may partially dissolve water dispersible granules or may result in storage stability issues (mold formation) in non-dispersible granules. Organic solvents used to dissolve active agents may also attack the organic polymer binders degrading granule strength characteristics.
Granular material may also be formed by agglomerating fibrous particles with powdered mineral components. In this case the agglomeration process forms granules by enabling the fibrous particles to “knit together.” Granules formed by this process are generally not as durable as granules produced with organic polymer binders.
Granular materials formed by agglomeration with organic polymer binders or by “knitting together” of fibrous materials use water as an essential ingredient to effect granulation, and this water must be driven off in a dryer to complete the agglomeration process. The residual water content in the granules following agglomeration is often described as “green pellet moisture.” Removal of “green pellet moisture” by drying accounts for a significant proportion of the energy required for production of these types of granules.